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Parker Hannifin
142 Aries User Guide
term is to anticipate position error and correct it before it becomes too large.
This increases damping and tends to make the system more stable.
If this term is too large, the response will be slowed to the point that the
system is over-damped.
Since the feedback device signal has finite resolution, the velocity accuracy
has a limit. Therefore, if the velocity feedback gain (SGV) is too high, the
errors due to the finite resolution are magnified and a noisy, or chattering,
response may be observed.
SGVF
Velocity Feedforward Gain
Type
Tuning
Product Rev
Syntax
<a_><!>SGVF<i>
Aries 2.0
Units
N/A
Range
Ø-5ØØ
Default
1ØØ
Response
SGVF: *SGVF1ØØ
See Also
DMTD, LJRAT
Use the SGVF command to set the velocity feedforward gain. Velocity
feedforward control improves position tracking performance when the system
is commanded to move at constant velocity. The velocity tracking error is
mainly attributed to viscous friction.
The SGVF value is multiplied by the commanded velocity calculated by the
Aries drive’s move profile routine to produce an estimated torque command
that gets added to the servo control signal. The value is normalized to the
current setting of both the motor and load viscous damping terms (DMTD) as
shown in the equation below.
commandvelocity DMTD torque velocity Estimated
100% valueSGVF
⋅
=
=
43421
Setting SGVF to one (1) theoretically produces zero (0) following errors during
the constant velocity portion of a move profile. This assumes that the drive or
motor are not being current limited, the values for viscous damping are
accurate and the models used for analysis are correct. The value of SGVF
can be adjusted from zero to as high as five (5) times (SGVF5) the theoretical
value.
Example
SGVF2 ; Set velocity feedforward to 200% of theoretical value